摘要
山东沂水地区紫苏花岗岩主要有 3种类型 ,分别为紫苏花岗闪长岩、紫苏石榴花岗闪长岩和紫苏奥长花岗岩。紫苏花岗岩中普遍存在有熔体交代结构 ,主要由残晶相矿物和结晶相矿物组成。对紫苏花岗岩及变质表壳中流体包裹体产状、成分的研究发现 ,富CO2 流体包裹体和富N2 流体包裹体均来自地幔深部。紫苏花岗岩的形成过程如下 :基性岩浆的底侵作用使本区经历了第一期麻粒岩相变质作用 ,地幔富CO2 流体包裹体的存在使系统a(H2 O)很低 (a(H2 O) =0 .1～ 0 .3) ,麻粒岩相变质作用没有产生熔融作用。幔源岩浆活动的逐渐停止 ,该区又经历了近等压降温的第二期麻粒岩相变质作用。此时 ,深源富CO2 流体作用减弱 ,水的活度增加 ,a(H2 O) =0 .6 5～ 0 .75 ,从而产生岩浆 ,新生岩浆对早期形成的变质矿物进行熔蚀交代作用 ,使早期形成的难熔变质矿物如紫苏辉石、石榴石、单斜辉石等呈残晶相 ,随着温度的降低岩浆基本在原地半原地结晶形成紫苏花岗岩。
Charnockites are classified into three types in the Yishui area, Shandong Province, namely: enderbite, garnet-enderbite and hypersthene-trondhjemite. Charnokites consist of restite mineral and neocrystallized minerals. The shape of relic minerals is mostly irregular and the crystal boundaries are crenulate. They usually occupy the interstitial position between the neocrystalline minerals. Neocrystalline minerals are usually euhedral-subhedral crystals. The processes of charnokite formation are as follows: The underplating of mantle magmatism had caused widespread amphibolite-facies prograde metamorphism (M_1) in the Yishui area. The addition of mafic magmas to the base of the crust and/or as intrusions into the crust made the crust moderately thickened. Subsequently, the intensive magmatism resulted in the local peak granulite-facies metamorphism (M_2). With the lower a(H_2O) in the system, there would be no melting at this stage. With the weakening of the mantle magmatism, the heated crust experienced near isobaric cooling, causing the second granulite-facies metamorphism (M_3). At the same time, with the a(CO_2) decreased and a(H_2O) increased, a large volume of crustal melting was thus generated. During the melting process, refractory minerals, such as garnet, hyphethene and clinopyroxene were preserved as relics. As the melts recrystallized, the euhedral-subhedral plagioclase and K-feldspar were formed, resulting in present feature of charnockites.
出处
《地学前缘》
EI
CAS
CSCD
2003年第3期257-267,共11页
Earth Science Frontiers
基金
国家自然科学基金重点项目 (4 0 2 3 40 48)
科学技术部基础项目 (3 3 0 0 1)
中国地质调查局项目 (2 0 0 113 90 0 0 18)
国家教育部博士学科点基金项目 (970 4910 4)
关键词
紫苏花岗岩
残晶相
形成过程
山东沂水
charnokite
restite minerals
processes of charnokite formation
Yishui area, Shandong Province
